Micro-electromechanical system (MEMS) pressure sensors are well known. For example, U.S. Pat. No. 4,236,137 to Kurtz, et al. discloses a semiconductor pressure transducer. U.S. Pat. No. 5,156,052 issued to Johnson, et al. also discloses a solid state pressure transducer. U.S. Pat. No. 6,006,607 issued to Bryzek, et al. discloses a pressure sensor that uses a piezoresistive device. U.S. Pat. Nos. 5,178,016 and 6,093,579 also discloses solid state pressure sensors. See also U.S. Pat. No. 8,881,596 entitled, “Semiconductor sensing device to minimize thermal noise,” which is owned by the Applicant of this application and which is also incorporated by reference in its entirety.
A well-known problem with prior art MEMS pressure sensors is pressure nonlinearity or “PNL.” PNL is a function of the silicon diaphragm's deflection. Diaphragm deflection, however, determines a MEMS pressure sensor's ability to detect small pressure changes. Unfortunately, as diaphragm deflection increases, so does output nonlinearity. See for example, U.S. pre-grant publication 20150330856, entitled, “PRESSURE SENSOR DEVICE WITH HIGH SENSITIVITY AND HIGH ACCURACY,” published Nov. 19, 2015, assigned to the same applicant and incorporated herein by reference in its entirety.
Sensitivity becomes more problematic due to a smaller diaphragm in a shrunken MEMS pressure sensor that is required to sense low pressures, i.e., pressures below about 100 kPa. A solid state piezoresistive pressure sensor that can be used at low pressures and which has a smaller diaphragm in a smaller die with an improved output linearity and which is more sensitive than those in the prior art would be an improvement.